This proposal requests support for a combined neurochemical and morphometric study of three types of neurological mutant mice in which cerebellar Purkinje cell loss occurs during 3 different stages of cerebellar development. The extent of Purkinje cell loss ranges from total in two mutants to about 75 percent in a third. Three different genetic processes are represented by these mutants in which Purkinje cell death occurs in infantile, juvenile, or adult stages. The proposed studies are designed to analyze the effects of Purkinje cell degeneration in these three diferent conditions on target cells in the deep nuclei and on two sets of Purkinje cell afferents, the climbing fibers from the inferior olive and the norepinephrine containing fibers from locus coeruleus. Results from the Purkinje cell deficient animals will be compared with a granule cell deficient mutant in which Purkinje cells are spared and with chimeric mice (tetraparental) in which variable percentages of normal wild-type Purkinje cells are mixed with mutant cells. The responses of targets and afferents in the diseases which occur at three stages in the developmental history of the cerbellum will be assessed through measurement of relevant neurotransmitter-related substances, by cell counts and by area measurement of neurons. Special emphasis will be focused on the noradrenergic system originating inlocus coeruleus. Examination of this system will include the measurement of endogenous transmitter, synthesizing enzyme, a metabolite related to physiological activity, synaptosomal uptake of 3H norepinephrine and catecholamine histofluorescence. This noradrenergic system will be examined in cerebellar cortex, deep nuclei and in areas unaffected by the genetic lesion but receiving projections from locus coeruleus such as hippocampus. This is a study of a circuit in brain in which one link is removed. As is the case in human diseases, a neuron can disappear at different stages during the development of the brain. We anticipate that the consequence of cell death will be different under these conditions in terms of the stability, activity and disposition of afferent neurons. The information gained from these studies is particularly valuable for the comprehension of human disease in which selectively vulnerable cell populations are killed and will contribute to our understanding of denervation placticity.